Synthesis and thermochemistry of SrB2O4·4H2O and SrB2O4

Two pure strontium borates SrB₂O₄·4H₂O and SrB₂O₄ have been synthesized and characterized by means of chemical analysis and XRD, FT-IR, DTA-TG techniques. The molar enthalpies of solution of SrB₂O₄·4H₂O and SrB₂O₄ in 1 mol dm⁻³ HCl(aq) were measured to be −(9.92 ± 0.20) kJ mol⁻¹ and −(81.27 ± 0.30) kJ mol⁻¹, respectively. The molar enthalpy of solution of Sr(OH)₂·8H₂O in (HCl + H₃BO₃)(aq) were determined to be −(51.69 ± 0.15) kJ mol⁻¹. With the use of the enthalpy of solution of H₃BO₃ in 1 mol dm⁻³ HCl(aq), and the standard molar enthalpies of formation for Sr(OH)₂·8H₂O(s), H₃BO₃(s), and H₂O(l), the standard molar enthalpies of formation of −(3253.1 ± 1.7) kJ mol⁻¹ for SrB₂O₄·4H₂O, and of −(2038.4 ± 1.7) kJ mol⁻¹ for SrB₂O₄ were obtained.     

Diaqua oxalato strontium(II) complex as a precursor for facile fabrication of Ag-NPs@SrCO3, characterization,optical properties,morphological studies and adsorption efficiency

Diaqua oxalato strontium(II) complex [Sr(C₂O₄)(H₂O)₂] was prepared via a precipitation reaction. Thermal treatment of the as-synthesized precursor at 550?°C resulted in formation of strontium carbonate (SrCO₃) nanocrystals. A new composite of silver nanoparticles decorated with strontium carbonate (Ag-NPs@SrCO₃) was fabricated by heating a mixture of silver oxalate and strontium carbonate in air at 150?°C for 2?h. The spectral, morphological and thermal properties of the materials have been studied using different physicochemical techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX), high-resolution transmission electron microscopy (HR-TEM), Fourier infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), diffrential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). From the Debye–Scherrer equation the calculated particle size of Sr(C₂O₄)(H₂O)₂], SrCO₃ and Ag-NPs@SrCO₃ are 62.1, 58.7, and 58.5?nm, respectively. The SEM and TEM images indicate tetragonal structure of [Sr(C₂O₄)(H₂O)₂] while SrCO₃ and Ag-NPs@SrCO₃ appeared as cubic structures. The calculated energy band gap of SrCO₃ and Ag-NPs@SrCO₃ using the Tauc equation are estimated at 5.9 and 4.7?eV, respectively. The adsorption capacity of the materials is tested for the adsorption of Congo red anionic dye and exhibited promising results. The adsorption capacity followed the order Ag-NPs@SrCO₃>SrCO₃>?[Sr(C₂O₄)(H₂O)₂] with efficiencies of 73.90, 67.55, and 60.50%, respectively.     

Thermal dehydration and decomposition of M[M(C2O4)2]·xH2O (x=3 forM=Sr(II) andx=6 forM=Hg(II))

Strontium(II) bis (oxalato) strontium(II) trihydrate, Sr[Sr(C₂O₄)₂]·3H₂O and mercury(II) bis (oxalato) mercurate(II) hexahydrate, Hg[Hg(C₂O₄)₂]·6H₂O have been synthesized and characterized by elemental analysis, reflectance and IR spectral studies. Thermal decomposition studies (TG, DTG and DTA) in air showed SrCO₃ was formed at ca. 500°C through the formation of transient intermediate of a mixture of SrCO₃ and SrC₂O₄ around 455°C. Sharp phase transition from γ-SrCO₃ to β-SrCO₃ indicated by a distinct endothermic peak at 900°C in DTA. Mercury(II) bis (oxalato) mercurate(II) hexahydrate showed an inclined slope followed by surprisingly steep slope in TG at 178°C and finally 98.66% of weight loss at 300°C. The activation energies (E ^*) of the dehydration and decomposition steps have been calculated by Freeman and Carroll and Flynn and Wall's method and compared with the values found by DSC in nitrogen. A tentative reaction mechanism for the thermal decomposition of Sr[Sr(C₂O₄)₂]·3H₂O has been proposed.     

Synthesis and Thermal Study of 8-Hydroxyquinoline Derivatives of the Alkaline Earth Metals I. Strontium Complexes

Strontium complexes of 5,7-dibromo-, 5,7-dichloro-, 7-iodo- and 5-chloro-7-iodo-8-hydroxyquinoline were precipitated from an aqueous ammonia and acetone medium. The complexes obtained were Sr[(C₉H₄ONBr₂)₂]·2.5H₂O; Sr[(C₉H₄ONCl₂)(OH)]·1.5H₂O; Sr[(C₉H₅ONI)₂]·5H₂O and Sr[(C₉H₄ONICl)(OH)]·1.25H₂O. The residues of their thermal decomposition were SrBr₂; a mixture of SrCl₂, SrCO₃ and SrO; SrCO₃ and SrCO₃, respectively. All were characterized by means of thermogravimetry, differential thermal analysis, complexometry with EDTA, atomic absorption spectroscopy, IR spectroscopy and X-ray diffraction. This revised version was published online in August 2006 with corrections to the Cover Date.     

The ion exchange of strontium on sodium titanate Na4Ti9O20.xH2O

The ion exchange behaviour of the exchanger Na₄Ti₉O₂₀.xH₂O was studied with particular emphasis on Sr²⁺ exchange. Titration of H₄Ti₉O₂₀.xH₂O with 0.1M [Sr/OH/₂+SrCl₂] solution yielded a strontium ion exchange capacity of 5.30 meq g^–1 corresponding well with the theoretical value. When strontium was absorbed on Na₄Ti₉O₂₀.xH₂O from neutral solutions, Sr₂Ti₉O₂₀.xH₂O was formed. This compound decomposed to SrTiO₃ and TiO₂ when heated to 870 °C. From alkaline solutions strontium was absorbed both as Sr/OH/⁺ and Sr²⁺ with the proportion of the former species increasing with pH. At pH 12.8 only exchange of Sr/OH/⁺ was observed and the exchanged form was Na₂/SrOH/₂Ti₉O₂₀.xH₂O. This compound decomposed to Na₂Ti₆O₁₃ and an unidentified strontium titanate when heated to 870 °C. Distribution coefficients were determined for alkali and alkaline earth metal ions as a function of pH. The selectivity sequence for alkaline earth metal ions was Ba>SrCa>Mg, and that for alkali metal ions was Cs>K>Li /pH 2–6/ and Li>Cs>K /pH 7/.     

Co(en)3[B4O5(OH)4]Cl·3H2O和[Ni(en)3][B5O6(OH)4]2·2H2O的合成、结构以及热力学性质

利用水热法合成了两种过渡金属配合物为模板剂的含水硼酸盐晶体Co(en)3[B4O5(OH)4]Cl·3H2O(1) 和 [Ni(en)3][B5O6(OH)4]2·2H2O (2),并通过元素分析、X射线单晶衍射、红外光谱及热重分析对其进行了表征。化合物1晶体结构的主要特点是在所有组成Co(en)33+, [B4O5(OH)4]2–, Cl– 和 H2O之间通过O–H…O、O–H…Cl、N–H…Cl和N–H…O四种氢键连接形成网状超分子结构。化合物2晶体结构的特点是[B5O6(OH)4]–阴离子通过O–H…O氢键连接形成沿a方向有较大通道的三维超分子骨架,模板剂[Ni(en)3]2+阳离子和结晶水分子填充在通道中。     

A2Ca[B4O5(OH)4]2·8H2O(A=Rb,Cs)硼氧酸盐复盐的合成与表征

硼氧酸盐晶体结构复杂，因此出现了许多具有特殊物理性能的晶体功能材料犤１，２犦，尤其是重稀碱金属硼氧酸盐（或复盐），如CsLiB６O１０犤３犦、LiRbB４O７犤４犦和CsB３O５（CBO）犤５犦都是非线性光学材料。一些学者对铷、铯的偏硼氧酸盐、四硼氧酸盐和五硼氧酸盐的合成、性质及晶体结构等进行过研究犤６～９犦。硼氧酸盐复盐，大多为碱金属和碱土金属、碱金属和碱金属及碱土金属和碱土金属的硼氧酸盐犤１０犦，如自然界存在的钠硼解石狖NaCa犤B５O６（OH）６犦·５H２O狚、硼钠镁石狖Na２Mg犤B６O８（OH）４犦２·６H２O…     

Untersuchungen im System SrO?SiO2?H2O

Investigation on the System SrO? SiO₂? H₂O On addition sodium silicate solutions to solutions of Sr(OH)₂, at room temperature strontium hydrogensilicates are precipitated which are always amorphous and contain silicate anions of various condensation degrees. At about 100°C at first also amorphous products are formed containing lower- and higher-molecular silicate anions. On standing of these precipitates at about 80°C under the mother liquor, however, cristallization occurs under complete degradation of the higher-molecular anions to monomeric resp. dimeric silicate anions. In dependence on the Na₂O: SiO₂ ratio of the sodium silicate solutions and on the Sr(OH)₂ concentrations the following crystalline compounds are formed: 1.25 SrO · 1 SiO₂ · 2 H₂O, 3 SrO · 2 SiO₂ · 3 H₂O and 3 SrO · 2 SiO₂ · 4 H₂O, with monomeric silicate anions; 2 SrO · 2 SiO₂ · 1.5 H₂O; 2 SrO · 2 SiO₂ · 2 H₂O, and 2 SrO · 2 SiO₂ · 3 H₂O, with dimeric anions.     

Crystallographic report: Crystal structure of the first alkaline earth metal compound with the antibacterial drug sulfasalazine: [Sr(H‐Sulf)(H2O)6](H‐Sulf)·3H2O

The structure of [Sr(H‐Sulf)(H₂O)₆](H‐Sulf)·3H₂O features a seven‐coordinated distorted capped octahedral geometry around strontium(II) with Sr? O distances ranging from 2.445(5) to 2.606(5) Å. Copyright © 2003 John Wiley & Sons, Ltd.     

Mechanochemical Synthesis and Characterization of Hydrated and Dehydrated Crystalline Strontium Terephtalates

A successful mechanochemical synthesis of strontium terephthalate trihydrate is described for the first time. The dehydration of Sr(C₈H₄O₄) · 3H₂O occurs at about 100 °C and results in a well‐defined strontium terephtalate, Sr(C₈H₄O₄), thermally stable up to 550 °C. Both compounds are not described so far in the literature. Their structures were solved by ab initio structure determination and subsequent Rietveld refinement of the powder diffraction data. Further methods like DTA‐TG, MAS NMR and FT‐IR spectroscopy, and BET measurements were used to characterize these compounds.     

Synthesis,Structural Characterization and Properties of Two Strontium Borates Constructed from Oxo Boron Clusters

Two strontium borates Sr₂[B₆O₉(OH)₄] (1) and Sr₂B₅O₉(OH)·H₂O (2), with acentric structures have been synthesized under hydro/solvothermal conditions. Compound 1 is reported for the first time in the strontium borates system, and it crystallizes in the monoclinic space group P2₁ with unit cell parameters a = 6.8445(5) Å, b = 8.7033(6) Å, c = 8.4632(6) Å, β = 100.581(6)°, V = 495.58(6) ų and Z = 2. Its structure consists of unusual borate layers of 3, 11-membered rings, which are interconnected via Sr–O ionic bonds and hydrogen bonds to generate a 3D supramolecular network. Compound 2 is a known strontium borate, crystallizing in the monoclinic space group C ₂ with a = 10.161 (13) Å, b = 7.965(4) Å, c = 6.393(11) Å, β = 128.0(2)°, V = 407.7(14) ų and Z = 2. Second-harmonic generation measurements on the powder samples reveal that 1 and 2 exhibits good SHG efficiency about 1.5 and 2 times that of KDP (KH₂PO₄) powder respectively.     

Calcium and strontium thio­sulfate,CaS2O3·6H2O and SrS2O3·5H2O

In contrast to former morphological studies, the results presented here show that calcium(II) thio­sulfate hexahydrate, CaS₂O₃·6H₂O, crystallizes centrosymmetrically in the pinacoidal class (point group ). The structure is characterized by chains, parallel to [100], of alternating S₂O₃ and Ca(H₂O)₆O₂ groups sharing common O atoms. The composition of each chain link is [Ca(H₂O)₆(S₂O₃)]. The geometry is analysed and compared in detail with the structural features of monoclinic strontium(II) thio­sulfate pentahydrate, SrS₂O₃·5H₂O, which forms layers, parallel to (100), of alternating S₂O₃ and Sr(H₂O)₄O₅ groups connected via common O atoms and O–O edges. Each layer contains [Sr(H₂O)₃O(S₂O₃)]_∞ as the unique repeat unit.     

Thermoanalytical investigation of some alkaline earth hydroxide hydrates on application as latent heat storage materials

Owing to their high specific melting enthalpy and the range of the melting temperatures the alkaline-earth hydroxide hydrates Ba(OH)₂·8H₂O and Sr(OH)₂·8H₂O are promising latent heat storage materials. The investigations of the melting and solidification behaviour of Sr(OH)₂·8H₂O and its mixtures with Ba(OH)₂·8H₂O, which had been performed by means of DTA and DSC methods in the closed system with a constant gross composition lead to statements on the melting temperature and specific melting enthalpyvs. concentration. Theoretical storage densities of 532 MJ/m³ are obtained for the mixture of Ba(OH)₂·8H₂O and Sr(OH)₂·8H₂O (80/20) and a value of 655 MJ/m³ can be achieved for Sr(OH)₂·8H₂O. The kinetics of rehydration to the octahydrates has a great influence on the storage temperature and storage density.     

Thermal decomposition kinetics of strontium oxalate

The thermal decomposition behavior in air of SrC₂O₄ · 1.25H₂O was studied up to the formation of SrO using DTA-TG-DTG techniques. The decomposition proceeds through four well-defined steps. The first two steps are attributed to the dehydration of the salt, while the third and fourth ones are assigned to the decomposition of the anhydrous strontium oxalate into SrCO₃ and the decomposition of SrCO₃ to SrO, respectively. The exothermic DTA peak found at around 300°C is ascribed to the recrystallization of the anhydrous strontium oxalate. On the other hand, the endothermic DTA peak observed at 910°C can be attributed to the transition of orthorhombic-hexagonal phase of SrCO₃. The kinetics of the thermal decomposition of anhydrous strontium oxalate and strontium carbonate, which are formed as stable intermediates, have been studied using non-isothermal TG technique. Analysis of kinetic data was carried out assuming various solid-state reaction models and applying three different computational methods. The data analysis according to the composite method showed that the anhydrous oxalate decomposition is best described by the two-dimensional diffusion-controlled mechanism (D₂), while the decomposition of strontium carbonate is best fitted by means of the three-dimensional phase boundary-controlled mechanism (R₃). The values of activation parameters obtained using different methods were compared and discussed.     

Zur Koordination des Aluminiums in den Calciumaluminathydraten 2 CaO · Al2O3 · 8 H2O und CaO · Al2O3 · 10 H2O

On the Coordination of Al in the Calcium Aluminate Hydrates 2 CaO · Al₂O₃ · 8 H₂O and CaO · Al₂O₃ · 10 H₂O By investigations with high-resolution ²⁷Al-NMR in solids it is shown that in the compound 2 CaO · Al₂O₃ · 8 H₂O the Al merely exist in octahedral coordination. According to this and considering its structural relationship with 4 CaO · Al₂O₃ · 19 H₂O the dicalcium aluminate hydrate is proposed to be formulated as [Ca₂Al(OH)₆][Al(OH)₃ (H₂O)₃]OH. Likewise for the compound CaO · Al₂O₃ · 10 H₂O the octahedral coordination of the Al is proved by ²⁷Al-NMR. This result corresponds with literature according to which a constitution as cyclohexaaluminate Ca₃[Al₆(OH)₂₄] · 18 H₂O is proposed.     

Mineral and microelement compositions of urinary stones

The mineral and microelement compositions of urinary stones from patients in various districts of the Novosibirsk region are analyzed. The mineral composition is determined using X-ray powder diffraction and vibrational spectroscopy. The microelement composition is identified using synchrotron radiation X-ray fluorescence analysis. Calcium oxalates (whewellite CaC₂O₄ · H₂O and weddellite CaC₂O₄ · 2H₂O) are the most frequent components of the urinary stones. Oxalate uroliths contain a variety of microelements in significant amounts. Phosphate uroliths, represented by hydroxylapatite Ca₅(PO₄)₃(OH) and struvite MgNH₄PO₄ · 6H₂O, account for about one-fifth of the collection. Apatite urinary stones contain maximal strontium amounts. The struvite uroliths have higher rubidium levels. Uric acid uroliths (C₅H₄N₄O₃) account for about 11% of the collection. Their strontium concentrations are minimal. The element composition of the urinary stones is a function of their mineral constituents, the environmental surroundings, and the metabolism specifics of the patient.     

Kristallstrukturen des Sr(OH)2 · H2O,Ba(OH)2 · H2O (o.-rh. und mon.) und Ba(OH)2 · 3 H2O

Crystal Structures of Sr(OH)₂ · H₂O, Ba(OH)₂ · H₂O (o.-rh. and mon.), and Ba(OH)₂ · 3 H₂O The crystal structures of Ba(OH)₂ · 3 H₂O (Pnma, Z = 4), γ-Ba(OH)₂ · H₂O (P2₁/m, Z = 2) and the isotypic Sr(OH)₂ · H₂O and β-Ba(OH)₂ · H₂O (Pmc2₁, Z = 2) were determined using X-ray single crystal data. Ba(OH)₂ · 3 H₂O and Ba(OH)₂ · H₂O mon. crystallize in hitherto unknown structure types. The structure of Ba(OH)₂ · H₂O mon. is strongly related to that of rare earth hydroxides M(OH)₃ with space group P6₃/m (super group of P2₁/m). The metal-oxygen distances are significantly shorter for OH^? ions (mean Ba—O bond lengths of all hydroxides under investigation 278.1 pm) than for H₂O molecules (289.9 pm). Corresponding to other hydrates of ionic hydroxides, the water molecules form strong hydrogen bonds to adjacent OH^? ions whereas the hydroxide are not H-bonded.     

Preparation of Hydrated Strontium Silicates from Silica Hydrogel Isolated from Serpentines and Their Thermal Transformations

Interaction between silica hydrogel isolated from serpentines (Mg(Fe))₆[Si₄O₁₀](OH)₈, sodium hydroxide NaOH, and strontium chloride SrCl₂ in aqueous medium was studied by DTA and X-ray powder diffraction (XRD). Stirring of the boiling aqueous suspension prepared from these reagents under the atmospheric pressure for 2 h yields hydrated strontium silicate species: Sr₃Si₂O₇ · 4H₂O and Sr₃Si₂O₇ · 3H₂O or their mixtures, whose heating to 810–825°C is accompanied by some phase transformations: strontium metasilicate Sr₃Si₃O₉ or strontium orthosilicate Sr₂SiO₄ is formed after bound water is removed in the range 250–350°C, and strontium silicate SrSiO₃ is formed at higher temperatures. Sr₂SiO₄ single phase is observed upon heat treatment to 700–750°C. The optimal molar ratio of the reagents was found to favor Sr₂SiO₄ formation.     

偏硼酸锶/碳酸锶复合催化剂光催化还原CO2生成CH4的研究

采用溶胶-凝胶法制备出SrB₂O₄和SrCO₃复合催化剂(SrB₂O₄/SrCO₃). 紫外光催化还原CO₂生成CH₄的实验证明, SrB₂O₄/SrCO₃复合催化剂的光催化活性已超过SrB₂O₄和TiO₂(P25)催化剂. 利用X 射线电子衍射(XRD)谱、透射电子显微镜(TEM)和等温氮气吸附-脱附分析确定了催化剂的晶相结构、粒子尺寸和比表面积.利用紫外-可见(UV-Vis)漫反射吸收光谱、X射线光电子能谱(XPS)的价带谱和荧光光谱(PL)确定了催化剂的能带结构, 结果表明: SrB₂O₄/SrCO₃复合催化剂异质结构有利于光生载流子的分离, 从而抑制了光生电子和光生空穴的复合, 提高了光生电子和光生空穴在固液界面参加光催化反应的利用率. 因此, SrB₂O₄/SrCO₃复合催化剂的紫外光催化活性得到了有效的提高.     

Synthesis,characterization, and catalytic properties of the Li-doped ZnO

It has demonstrated that there are major advantages and synergistic effects on flame retardancy in using a combination of borates with magnesium hydroxide. In this paper, a novel 2MgO·B₂O₃·1.5H₂O–Mg(OH)₂ nanocomposite has been controllably prepared by in situ hydrothermal reaction, and the formation mechanism of the nanocomposite was proposed. As a comparison, 2MgO·B₂O₃·1.5H₂O nanobelt and Mg(OH)₂ nanosheet were also prepared. All samples were characterized by XRD, FT-IR, TG, SEM, TEM and HRTEM. Furthermore, their flame-retardant properties were investigated by thermal analysis method and oxygen index method, demonstrating that the flame retardancy of nanocomposite is significantly higher than that of single 2MgO·B₂O₃·1.5H₂O or Mg(OH)₂. The possible flame retarding mechanism has been proposed. It can be predicted that this nanocomposite could serve as a potential flame retardant.